Overvoltage protection device

Abstract: An overvoltage protection device (20) connected between an AC plug (12) and an electronic device (11), comprises a first AC pattern (22, 32, 42, 52) having first and second concave circular arc sections (22a, 22b) and a first peak point (22c, 32b, 42c, 52b), a second AC pattern having third and fourth concave circular arc sections (23a, 23b) and a second peak point (23c), and a frame ground pattern (24, 34, 44, 54) having a fifth concave circular arc section (24a) with the first peak point (22c, 32b, 42c, 52b) as a center and a sixth concave circular arc section (24b) with the second peak point (23c) as a center, both ends of the fifth concave circular arc section (24a) being located at centers of the first and second concave circular arc sections (22a, 22b), and both ends of the sixth concave circular arc section (24b) being located at centers of the third and fourth concave circular arc sections (23a, 23b). If an overvoltage is applied to any of the first and second AC patterns (22, 23), a discharge occurs across any of the AC pattern (22, 23) and the frame ground pattern (24, 34, 44, 54), allowing the overvoltage to escape to ground. It is thus possible to prevent destruction of the electronic device (11) resulting from the application of the overvoltage.

Description: The present invention relates to an overvoltage protection device which can prevent an electronic apparatus from being destroyed due to an overvoltage, such as a surge, caused by lightning, etc. Generally, an electronic apparatus is, when being used, supplied with a commercial power supply. In the case where lightning strikes a generating station, a transmission station, a substation, etc., a very high overvoltage (surge voltage) is momentarily applied to a power supply line through induction, sometimes causing the destruction of some element of the electronic apparatus. In the prior art, the electronic device has been protected by an arrester from such an overvoltage. FIG. 1 is a block diagram showing a conventional overvoltage protection device using arresters. Power is supplied to an electronic device 1 by inserting an AC plug 2 of the electronic device 1 into an AC outlet 3 provided in a wall, a floor, etc., of a room. The AC outlet 3 has AC terminals 3a and 3b connected to commercial power supply lines (not shown) and a frame ground terminal 3c. The AC plug 2 has AC poles 2a and 2b connected to AC terminals 3a and 3b of the AC outlet and a frame ground pole 2c connected (grounded) to the frame ground terminal 3c of the AC outlet 3 through arresters 4 and 5. In such a conventional device, when any overvoltage occurs on the commercial power supply line and is applied to any one of the AC poles 2a and 2b of the AC plug 2, a corresponding arrester is operated (turned ON), so that short-circuiting occurs between the frame ground electrode 2c of the AC plug 2 and any corresponding one of the AC poles 2a and 2b of the AC plug 2 which is applied with the overvoltage. As a result, the overvoltage escapes to ground and no overvoltage is supplied to the electronic device 1. The arrester has the disadvantage of being normally expensive and, further, its operation start voltage cannot be set at too high a level. Even if, therefore, any overvoltage is applied to the electronic device to a practically unaffected extent, a power supply to the electronic device is sometimes interrupted. This offers the disadvantage of the power supply being frequently interrupted to an unnecessary extent. Since, as described above, the arrester is employed to protect an electronic device from an overvoltage such as a lightning surge, the overvoltage protection device involves high costs and, further, an unnecessary power supply stoppage has been encountered. The power supply stoppage while the electronic device being operated is not desirable and, sometimes, the electronic device functions abnormally. Prior art document AU-B-532 286 discloses an overvoltage lightning protection device comprising two electrodes or conductors with peak points spaced a given distance apart on an insulating substrate. The electrodes have a tooth shape. Since the distance between the two electrodes periodically varies along the tooth an uniform discharge cannot be expected. It is an object of the present invention to provide an overvoltage protection device which can be manufactured at low costs. A related object of the present invention is to provide an overvoltage protection device which can freely set a voltage at any given level which starts the stoppage of a power supply to the electronic device. To solve this object the present invention provides an overvoltage protection device as specified in claim 1. Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the present invention and, together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the present invention in which: FIG. 1 is a block diagram showing a conventional overvoltage protection device using arresters; FIG. 2 is a block diagram showing an overvoltage protection device according to a first embodiment of the present invention; FIG. 3 is a block diagram showing an overvoltage protection device according to a second embodiment of the present invention; FIG. 4 is a plan view showing an overvoltage protection device according to a third embodiment of the present invention; and FIG. 5 is a plan view showing an overvoltage protection device according to a fourth embodiment of the present invention. A preferred embodiment of an overvoltage protection device according to the present invention will now be described with reference to the accompanying drawings. FIG. 2 is a block diagram showing an arrangement of a first embodiment of the present invention. In the first embodiment, power is supplied to the electronic device 11 by inserting an AC plug 12 of an electronic device 11 into an AC outlet 13 mounted on a wall, a floor, etc., of a room. The AC outlet 13 has AC terminals 13a and 13b connected to commercial power supply lines (not shown) and a frame ground terminal 13c grounded. An overvoltage protection device 20 is connected between the AC plug 12 and the electronic device 11 and has three kinds of copper foil patterns on an insulating substrate 21, that is, first and second AC patterns 22 and 23 and a frame ground pattern 24. Though not shown, a solder layer is formed on the copper foil to prevent the copper foil from being broken due to discharge. The AC plug 12 has AC poles 12a and 12b connected to the AC terminals 13a and 13b of the AC outlet 13 and also to the first and second AC patterns 22 and 23 and an AC pole 12c connected to the frame ground terminal 13c of the AC outlet 13 and also to the frame ground pattern 24. It is to be noted that the AC poles 12a and 12b of the AC plug 12 may sometimes be connected to the AC terminals 13b and 13a, respectively, in the AC outlet 13. The AC patterns 22 and 23 have the same configuration and are symmetrically arranged relative to a frame ground pattern 24. That is, the AC patterns 22 and 23 are so formed as to provide a deformed rectangular pattern in which one of longer sides facing the frame ground pattern 24 is divided into two parts and these half parts are replaced by two concave circular arc sections 22a, 22b; and 23a, 23b, respectively. Each concave circular arc section has a center at a perpendicular bisector of the half part and a radius "r" passing through the junctions of two circular arc sections or through the corner of the rectangular. It is to be noted that the junction of the adjacent circular arc sections 22a and 22b is referred to as the peak point 22c and the junction of the adjacent circular arc sections 23a and 23b, as a peak point 23c. The frame ground pattern 24 has the same configuration at those areas facing the AC patterns 22 and 23. That is, the frame ground pattern 24 is so formed as to provide a deformed rectangular pattern in which longer sides facing the AC patterns 22 and 23 are replaced by two concave circular arc sections 24a and 24b, respectively. Each concave circular arc section has a center at a perpendicular bisector of the longer side of the rectangular and a radius "r" passing through the corners of the rectangular. The four corners of the deformed rectangular pattern provide four peak points 24c, 24d, 24e and 24f. Thus the respective concave circular arc sections have the same radius, it can be expressed that the patterns 22, 23, and 24 are arranged as will be set out below. The AC patterns 22 and 23 are so located that the circular arc sections 22a and 22b face the circular arc sections 23a and 23b, respectively, with the frame ground pattern 24 formed therebetween. As a result, the distances defined below are all equal to the radius "r" of the concave circular arc sections. (1) The distance between each point on the concave circular arc section 22a of the AC pattern 22 and the peak point 24c of the frame ground pattern 24. (2) The distance between each point on the concave circular arc section 22b of the AC pattern 22 and the peak point 24d of the frame ground pattern 24. (3) The distance between the peak point 22c of the AC pattern 22 and each point on the concave circular arc section 24a of the frame ground pattern 24. (4) The distance between each point on the concave circular arc section 23a of the AC pattern 23 and the peak point 24e of the frame ground pattern 24. (5) The distance between each point on the concave circular arc section 23b of the AC pattern 23 and a peak point 24f of the frame ground pattern 24. (6) The distance between the peak point 23c of the AC pattern 23 and each point on the concave circular section 24b of the frame ground pattern 24. From these it follows that (a) The concave circular arc section 22a of the AC pattern 22 corresponds to a circular arc section having the radius "r" with a peak point 24c of the frame ground pattern 24 as a center; (b) The concave circular arc section 22b of the AC pattern 22 corresponds to a circular arc section having the radius "r" with the peak point 24d of the frame ground pattern 24 as a center; (c) The concave circular arc section 23a of the AC pattern 23 corresponds to a circular arc section having the radius "r" with the peak point 24e of the frame ground pattern 24 as a center; (d) The concave circular arc section 23b of the AC pattern 23 corresponds to a circular arc section having the radius "r" with the peak point 24f of the frame ground pattern 24 as a center; (e) The concave circular arc section 24a of the frame ground pattern 24 corresponds to a circular arc section having the radius "r" with the peak point 22c of the AC pattern 22 as a center; and (f) The concave circular arc section 24b of the frame ground pattern 24 corresponds to the circular arc section having the radius "r" with the peak point 23c of the AC pattern 23 as a center. The operation of this embodiment thus arranged will be explained below. At a normal time, a commercial AC power is supplied to the electronic device 11 through the AC outlet 13, AC plug 12, and AC patterns 22 and 23. When any abnormal overvoltage is induced in the AC power supply line due to an effect of lightning involved, the following phenomena occur in the overvoltage protection apparatus. (I) When the AC patterns 22 and 23 are "hot" and "neutral" and any negative overvoltage occurs, a discharge is developed from the peak point 22c of the AC pattern 22 toward the concave circular arc section 24a of the frame ground pattern 24. (II) When the AC patterns 22 and 23 are "hot" and "neutral" and any positive overvoltage occurs, a discharge is developed from the peak points 24c and 24d of the frame ground pattern 24 toward the concave circular arc sections 22a and 22b of the AC pattern 22. (III) When the AC patterns 22 and 23 are "neutral" and "hot" and any negative overvoltage occurs, a discharge is developed from the peak point 23c of the AC pattern 23 toward the concave circular arc section 24b of the frame ground pattern 24. (IV) When the AC patterns 22 and 23 are "neutral" and "hot" and any positive overvoltage occurs, a discharge is developed from the peak points 24e and 24f of the frame ground patter 24 toward the concave circular arc sections 23a and 23b of the AC pattern 23. That is, short-circuiting occurs between the AC patterns 22 and 23 in the "hot" state and the frame ground pattern 24 whereby almost all overvoltage goes to ground. Here a discharge start voltage, that is, a lowest voltage at which a discharge occurs between the AC patterns 22 and 23 on one hand and the frame ground pattern on the other hand is determined by a distance (here all the distances are set to be constant, that is, "r") between the peak point 22c and the concave circular arc section 24a, the peak point 23c and the concave circular arc section 24b, the peak point 24c and the concave circular arc section 22a, the peak point 24d and the concave circular arc section 22b, the peak point 24e and the concave circular arc section 23a, and the peak point 24f and the concave circular arc section 23b. In a practical case, the discharge start voltage is of the order of 1 kV at the distance "r" of 1 mm. Thus, at the distance "r" of 4 mm for instance, the discharge start voltage is of the order of 4 kv. It is, therefore, possible to set the discharge start voltage at a desired level. The discharge start voltage can be set at a greater level by setting, at a greater value, the distance "r" between the AC patterns 22 and 23 on one hand and the frame ground pattern 24 on the other hand. Further, these three patterns can be readily manufactured at low costs by printing them on a printed circuit board, etc. Since the discharge start voltage can be set by the distance "r" between the AC patterns 22 and 23 on one hand and the frame ground pattern 24 on the other hand, it is possible to readily realize discharge start voltages of a varying level. Since the discharge occurs between those areas of uniform distance ("r"), a stable discharge is developed at all times. Further, a uniform discharge current flows at all points along the concave circular arc section without being concentrated locally so that it allows fatigue to be distributed only along the concave circular arc section involved. The first embodiment may be modified such that those dotted hatched areas in FIG. 2 are omitted. FIG. 3 is a block diagram showing an arrangement according to a second embodiment of the present invention including an overvoltage protection device 30 and insulating substrate 31. The overvoltage protection device 30 of the second embodiment is the same as that of the first embodiment in terms of their principle, though being different from that of the latter embodiment in terms of the configurations of their AC patterns 32 and 33 and their arrangement. In the second embodiment, first and second AC patterns 32 and 33 are arranged one to the left and one to the right with a frame ground pattern 34 located to face these AC patterns. The AC patterns 32 and 33 have concave circular arc sections 32a and 33a, respectively, having radiuses "r" with peak points 34c and 34d of the frame ground pattern 34 as centers, respectively. The frame ground pattern 34 has a pair of concave circular arc sections 34a and 34b having radiuses "r" with adjacent peak points 32b and 33b of the AC patterns 32 and 33 as their centers, respectively. The overvoltage protection device 30 performs the same effect as the first embodiment. The second embodiment may be modified such that those pattern areas indicated by the dotted hatched areas in FIG. 3 are omitted. In this case, the frame ground pattern 34 may be separated into two frame ground patterns or the two concave circular arc sections 34a and 34b may be directly joined in a side-by-side fashion, as indicated by the AC patterns 22 and 23 of the first embodiment in FIG. 2, with their joined hatched areas omitted. In the latter case, the distance between the two AC patterns 32 and 33 is narrowed by an extent corresponding to that joined hatched area between the two frame ground patterns. FIG. 4 is a plan view showing three patterns on a substrate 41 of an overvoltage protection device 40 according to a third embodiment of the present invention. Like the second embodiment, the third embodiment is so configured that first and second AC patterns 42 and 43 of the same configuration are arranged one to the right and one to the left with a frame ground pattern 44 located to face the first and second AC patterns 42 and 43. The AC pattern 42 has two side-by-side concave circular arc sections 42a and 42b having a radius "r" each and the AC pattern 43 has two side-by-side concave circular arc sections 43a and 43b having a radius "r" each. The frame ground pattern 44 has a concave circular arc sections 44a and 44b having radiuses "r" with peak points 42c and 43c of the AC patterns 42 and 43 as their centers, respectively. The ends of the concave circular arc section 44a are peak points 44c and 44d providing the centers of those concave circular arc sections 42a and 42b of the AC pattern 42. The ends of the concave circular arc section 44b are peak points 44e and 44f providing the centers of those concave circular arc sections 43a and 43b of the AC pattern 43. The overvoltage protection device of the third embodiment also obtains the same effect as the aforementioned embodiments. The third embodiment may be modified by omitting those dotted hatched areas in FIG. 4. FIG. is a plan view showing three patterns on a substrate 51 of an overvoltage protection device 50 according to a fourth embodiment of the present invention. The fourth embodiment, like the first embodiment, is so configured that first and second AC patterns 52 and 53 are symmetrically arranged with a frame ground pattern 54 as a center. The AC patterns 52 and 53 have concave circular arc sections 52a and 53a, respectively, having radius "r" each. Both ends of the concave circular arc section 52a provide peak points 52b and 52c and both ends of the concave circular arc section 53a, peak points 53b and 53c. The frame ground pattern 54 has concave circular arc sections 54a, 54b, 54c, and 54d having radiuses "r" with the peak points 52b, 52c, 53b and 53c as their centers, respectively. A junction of the concave circular arc sections 54a and 54b of the frame ground pattern 54 provides a peak point 54e corresponding to the center of the concave circular arc section 52a. The junction of the concave circular arc sections 54c and 54d provides a peak point 54f corresponding to the center of the concave circular arc section 53a. The overvoltage protection device of the fourth embodiment obtains the same effect as the previous embodiment. According to the present invention, as set out above, it is possible to prevent any overvoltage which may occur on the power supply line from being applied to the electronic device through the utilization of a discharge between the AC patterns, on one hand, connected to the AC poles of the AC plug and the frame ground pattern, on the other hand, connected to the frame ground pole of the AC plug. Since the two patterns both have a pair of peak point and concave circular arc section and the concave circular arc section corresponds to a given circular arc section of a given radius with the peak point of an opposing pattern as a center, any discharge occurs at all points on the concave circular arc section at an equal distance from the peak point toward the concave circular arc section. As a result, the discharge occurs uniformly on all points on the opposing concave circular arc section without involving local fatigue along the whole concave circular arc section. Further, the discharge start voltage can be set by varying the radius of the concave circular arc section. It is thus possible to realize an overvoltage protection device ingeniously against the withstand voltage of the electronic device. Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the present invention in its broader aspects is not limited to the specific details, representative devices, and illustrated examples shown and described herein. Accordingly, various modifications may be made without departing from the scope of the general inventive concept as defined by the appended claims. For example, in the above-mentioned embodiments, both of the AC patterns connected to the AC poles 12a and 12b of the AC plug 12 have a pair of peak point and concave circular arc section since it is uncertain that any one of the AC poles 12a and 12b of the AC plug 12 is brought to a "hot" or a "neutral" state. If, among the AC poles 12a and 12b of the AC plug 12, that pole connected to the "hot" line is fixed, neither the peak point nor the concave circular arc section is required for that pattern connected to the "neutral" line. There occurs no discharge between the frame ground pattern and the AC pattern connected to the "neutral" line. That is, it is not necessary to provide an AC pattern connected to the "neutral" line. Further, a negative overvoltage normally occurs at the stroke of lighting. For the overvoltage being a negative one, therefore, no discharge is developed from the frame ground pattern toward the AC pattern and it is, therefore, not necessary to provide any peak point to the frame ground pattern and any concave circular arc section to the corresponding AC pattern. In a practical application, however, a positive overvoltage may sometimes occur due to an effect resulting from the inductive component, etc., on a power transmission line and it is preferable to provide for the occurrence of both the positive and negative overvoltage as set out above. In place of a single overvoltage protection device, more overvoltage protection devices may be provided so that they are connected in series.

Claims: An overvoltage protection (20, 30, 40, 50) device for connection between an electronic device and a power supply outlet having a power supply pole and a ground pole, the power supply pole being connected to a power supply line, comprising: an insulating substrate (21, 31 , 41, 51); a first conductive member (22, 32, 42, 52) formed on the insulating substrate (21, 31, 41, 51) and having a first peak point (22c, 32b, 42c, 52b); and a second conductive member (24, 34, 44, 54) formed on the insulating substrate (21, 31, 41, 51), characterized in that said first conductive member (22, 32, 42, 52) is connected to the power supply pole and the electronic device, and said second conductive member (24, 34, 44, 54) is connected to the ground pole and has a first concave circular arc section (24a, 34a, 44a, 54a) of a given radius with the first peak point as a center. The device according to claim 1, characterized in that said first conductive member (22, 32, 42, 52) has a second concave circular arc section (22a, 32a, 42a, 52a) of a given radius; and said second conductive member (24, 34, 44, 54) has a second peak point (24c, 34c, 44c, 54e) located at the center of the second concave circular arc section (22a, 32a, 42a, 52a). The device according to claim 1 or 2, characterized in that the first and the second conductive members comprise first and second copper foils. The device according to claim 2, comprising first and second power supply poles (12a, 12b) and the ground pole (12c), the first and the second power supply poles being connected to an AC power supply line, characterized in that the first conductive member is connected to the first power supply pole; the first peak point (22c, 32b, 42c, 52b) is located at one end of the second concave circular arc section (22a, 32a, 42a, 52a); a third conductive member (23, 33, 43, 53) is formed on the insulating substrate, connected to the second power supply pole and comprising a third peak point (23c, 33b, 43c, 53b) located at one end of a third concave circular arc section (23a, 33a, 43a, 53a); and the second conductive member (24, 34, 44, 54) has the second peak point (24c, 34c, 44c, 54e) located at one end of the first concave circular arc section (24a, 34a, 44a, 54a), a fourth concave circular arc section (24b, 34b, 44b, 54c) of the given radius with the third peak point (23c, 33b, 43c, 53b) as a center, and a fourth peak point (24e, 34d, 44e, 54f) located at one end of the fourth concave circular arc section (24b, 34b, 44b, 54c). The device according to claim 4, characterized in that said first conductive member (22, 42) further comprises a fifth concave circular arc section (22b, 42b) connected to the second concave circular arc section (22a, 42a) at the first peak point (22c, 42c) and having the given radius with the other end (24d, 44d) of the first circular arc section (24a, 44a) as a center; and said third conductive member (23, 43) further comprises a sixth concave circular arc section (23b, 43b) connected to the third concave circular arc section (23a, 43a) at the third peak point (23c, 43c) and having the given radius with the other end (24f, 44f) of the fourth concave circular arc section (24b, 44b) as a center. The device according to claim 4, characterized in that said first conductive member (52) further comprises a fifth peak point (52c) located at the other end of the second concave circular arc section (52a); said third member (53) further comprises a sixth peak point (53c) located at the other end of the third concave circular arc section (53a); and said second member (54) further comprises a seventh concave circular arc section (54b) of the given radius with the fifth peak point (52c) as a center and an eighth concave circular section (54d) of the given radius with the sixth peak point (53c) as a center. The device according to claim 4, characterized in that the first, the second, and the third members comprise first, second, and third copper foils.

Inventors: TSUCHIDA YUKIO, YOSHIDA SHIGERU, TSUCHIDA, YUKIO, YOSHIDA, SHIGERU
Applicants: NICHICON CORP, TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA, NICHICON CORPORATION
Application year: 1994
Main classification: H01T4
IPC codes: H01T4, H02H9